Common causes of corrosion in stainless steel

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1. Chemical corrosion 1.1 Surface contamination: Oil, dust, as well as acids, alkalis, salts, etc., attached to the surface of the workpiece can, under certain conditions, turn into corrosive agents. These agents react chemically with certain components in the stainless steel, resulting in chemical corrosion and rusting. 1.2 Surface scratches: Various scratches damage the passivation film, reducing the protective capacity of stainless steel and making it more prone to reacting with chemical agents, thereby causing chemical corrosion and rusting. 1.3 Cleaning: If cleaning is not thorough after pickling and passivation, residual liquids remain and cause direct corrosion of the stainless steel parts (chemical corrosion). 2. Electrochemical corrosion 2.1 Carbon steel contamination: Scratches caused by contact with carbon steel components, together with the formation of a galvanic cell with corrosive agents, lead to electrochemical corrosion. 2.2 Cutting: The attachment of substances prone to rusting such as slag and spatter, together with corrosion agents, forms a galvanic cell that leads to electrochemical corrosion. 2.3 Roasting effect: The composition and microstructure of the area heated by the flame become non-uniform, which forms a galvanic cell with the corrosive medium, leading to electrochemical corrosion. 2.4 Welding: Physical defects in the welding area (undercut, pores, cracks, lack of fusion, incomplete penetration, etc.) and chemical defects (coarse grains, chromium-deficient grain boundaries, segregation, etc.) form a galvanic cell with corrosive agents, leading to electrochemical corrosion. 2.5 Material: Chemical defects in stainless steel (such as uneven composition, impurities like S and P) and surface physical defects (such as porosity, sand holes, cracks, etc.) facilitate the formation of a galvanic cell with corrosive agents, leading to electrochemical corrosion. 2.6 Passivation: Poor passivation effects resulting from acid washing lead to an uneven or thin passivation film on the stainless steel surface, making it prone to electrochemical corrosion. 2.7 Cleaning: The remaining acid pickling and passivation residues, along with the products of chemical corrosion formed with the stainless steel, cause electrochemical corrosion in the stainless steel components.